1. Technical Field
The present disclosure relates to an antenna apparatus, and more particularly, relates to a small antenna apparatus operable in multiple bands. The present disclosure also relates to a communication apparatus and an electronic device, provided with such an antenna apparatus.
2. Description of Related Art
In recent years, wireless services using wireless communication apparatuses, such as mobile phones and smartphones, have widely popularized. As these wireless services have been sophisticated, it is required to improve communication quality and communication speed. Accordingly, each country plans to adopt a new communication scheme, LTE (Long Term Evolution) or LTE-Advanced, and to widen a frequency band to be used.
A new communication system such as LTE is added to a conventional 3G Wireless Wide Area Network, which in turn increases the number of frequency bands to be supported by a single wireless communication apparatus. In general, the UHF (Ultra High Frequency) band, which is advantageous for radio wave propagation, is wanted above all. Hence, each country plans to allocate new frequency bands, e.g., 704 to 746 MHz, 746 to 787 MHz, 1427.9 to 1500.9 MHz, 2.3 to 2.4 GHz, and 2.5 to 2.69 GHz, etc.
By providing a wireless communication apparatus with an antenna apparatus supporting the above-described various frequency bands allocated and used in each country, the antenna apparatus is expected to be more usable, e.g., international roaming becomes possible. Therefore, there is an increasing demand for achieving the multiband and wide band operation of an antenna apparatus.
As prior-art antenna apparatuses aiming to achieve multiband and wide band operation, the following antenna apparatuses are known.
An antenna apparatus of PCT International Publication WO 2009/031229 A is provided with: a first conductive wire; a second conductive wire connected to and intersecting the first conductive wire; a third conductive wire parallel to the first conductive wire, and connected to and intersecting the second conductive wire; a fourth conductive wire connected to and intersecting the third conductive wire; and a first planar conductive plate connected to one or two of the first, second, third, and fourth conductive wires, and arranged in a region surrounded by three of the first, second, third, and fourth conductive wires. In addition, an edge of the first planar conductive plate is parallel to the first conductor not connected to the first planar conductive plate.
An antenna apparatus of US Patent Application Publication No. 2009/0256763 A is a multiband folded loop antenna provided with a dielectric substrate, a ground plane, a radiating portion, and a matching circuit. The ground plane is located on the dielectric substrate, and has a grounding point. The radiating portion includes a supporter, a loop strip, and a tuning patch. The loop strip has a length about half wavelength of the antenna's lowest resonant frequency. The loop strip has a feeding end and a grounding end, and the grounding end is electrically grounded to the grounding point on the ground plane. The loop strip is folded into a three-dimensional structure, and is supported by the supporter. The tuning patch is electrically connected to the loop strip. The matching circuit is located on the dielectric substrate, with one terminal electrically connected to the feeding end of the loop strip and another terminal to a signal source.
An antenna apparatus of Japanese Patent Laid-open Publication No. 2008-177668 has a feed element portion, a folded element portion, and an open-end element portion. The feed element portion is fed at a feed point on a substrate. The feed element portion is formed to extend from the feed point to a first branch point, with a width “d”. The folded element portion branches from the feed element portion at the first branch point, and is folded at a folding point, and grounded at a ground end. The open-end element portion branches from the feed element portion at a second branch point, and is terminated at an open end. Both sides of the folding point on the folded element portion are short-circuited at a short circuit point between the first branch point or the ground end and the folding point.
An antenna apparatus of US Patent Application Publication No. US 2010/0271271 A is provided with a high-frequency radiator, a low-frequency radiator, a feeding connecter, and a grounding connecter. The feeding connecter electrically connects one terminal of the high-frequency radiator and the low-frequency radiator, to a feeding point. The grounding connecter electrically connects the other terminal of the high-frequency radiator and the low-frequency radiator, to a ground. The feeding connecter forms a first folded loop antenna including the high-frequency radiator and the grounding connecter, and resonating at a first frequency band. The feeding connecter forms a second folded loop antenna including the low-frequency radiator and the grounding connecter, and resonating at a second, a third, and a fourth frequency band. The first and second folded loop antennas are folded to form a three-dimensional structure.
An antenna apparatus of Japanese Patent Laid-open Publication No. 2010-087752 has a radiation electrode and a parasitic electrode. The radiation electrode is provided with a U-shaped folded strip electrode, having one end connected to a feed point and the other end as an open end, and supports a fundamental frequency band and harmonic frequency bands. The parasitic electrode is formed on the same plane as the radiation electrode, separated from the radiation electrode by a certain distance so as to be capacitively coupled to the folded portion of the radiation electrode, and connected to the ground.